Hydrofluorocarbons are useful as etching gases for the microfabrication of semiconductors, liquid crystals, and the like. In particular, methyl fluoride (CH3F) is drawing attention as an etching gas for forming state-of-the-art microstructures.
A known method for producing methyl fluoride is, for example, a method in which a mixed gas containing methyl fluoride and acid fluoride is obtained by pyrolyzing a starting compound in a gas phase (PTL 1).
In the above process, as a method for separating methyl fluoride and acid fluoride contained in the obtained mixed gas, PTL 1 proposes a method comprising cooling the mixed gas to separate it into a gas component and a liquid component, the gas component comprising a low-boiling-point component that contains methyl fluoride (boiling point: −79° C.) as a main component, and the liquid component comprising a high-boiling-point component that contains acid fluoride (e.g., 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride (boiling point: 32° C.) as a main component and may further contain unreacted starting compounds (1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether (boiling point: 68.5° C.) etc.).
Further, as another separation method, PTL 1 also proposes a method comprising bringing the obtained mixed gas into contact with water, an aqueous alkaline solution, or the like to dissolve the acid fluoride in an aqueous phase and remove the same. In this case, the use of an alcohol instead of water or an aqueous alkaline solution is also proposed. Bringing the mixed gas into contact with an alcohol to produce an ester makes combustion treatment easier. In a conventional method, the thus-obtained gas containing a large amount of methyl fluoride was further subjected to a rectification operation to purify the methyl fluoride.